1. Field of the Invention
The present invention relates to a device which is provided in an electronic still video camera, for example, and which keeps a visible image corresponding to an optical image obtained through a photographing lens, and which generates an image signal in accordance with the visible image.
2. Description of the Related Art
Conventionally, silver halide photographic material is generally used as a material for recording an optical image. Silver halide photographic material has high optical sensitivity and high resolution, and the economical efficiency thereof is excellent. However, silver halide photographic material has drawbacks in that not only is the developing process cumbersome but also a visible image cannot be obtained at the same time as photography. A dry-type developing method has been developed to simplify the developing process. However, simultaneous development in which a visible image is obtained upon photography is impossible in the dry-type developing method.
On the other hand, as non-silver-halide photographic materials, there are known electrophotographic materials, diazo type photographic materials, free-radical photographic materials and so on. In these materials, however, there is no material which has advantageous characteristics like silver halide photographic material, while being able to simultaneously develop and keep a visible image. Note that, electrophotographic materials have been used mainly in copying machines, since they can perform dry-type development and can simultaneously develop an electrostatic latent image, which is obtained by exposure, using toner.
In such electrophotographic materials, recently, a photographic material has been developed in which a recording medium made of the photographic material is electronically and directly developed similarly to a silver halide photographic material, so that the developed visible image can be immediately seen or recorded. Such a recording medium, in which a visible image is electronically developed, is referred to as an electro-developing recording medium in this specification.
Japanese Unexamined Patent Publication No. 5-2280, for example, discloses a recording medium which is a combination of an electrostatic information recording medium and an electric charge keeping medium, the electrostatic information recording medium having a photoconducting layer and an inorganic oxide material layer, and the electric charge keeping medium having a liquid crystal display. In this structure, when the electrostatic information recording medium is exposed while an electric voltage is applied to the electrostatic information recording medium and the electric charge keeping medium, an electric charge in accordance with the amount of incident light is generated in the electrostatic information recording medium. Since the intensity of an electric field applied to the liquid crystal display facing the electrostatic information recording medium varys in accordance with the generated electric charge, an image corresponding to the amount of light distribution is indicated or developed on the liquid crystal display.
Japanese Unexamined Patent Publication No. 5-150251 discloses a dispersion type liquid crystal display in which an image indicated on the liquid crystal display is kept, even if the electric field applied to the liquid crystal display is removed.
Conventionally, however, there is no optical mechanism such as a camera in which an electrophotographic material, by which simultaneous development can be performed, is used. Therefore, it has been desired to develop a device by which an image obtained by the electrophotographic material is converted into an electric signal, for example, and is outputted from the device.